Installations for this purpose are already known and are used for example, for the discharge of vapours and smoke from central heating plants into the atmosphere. These installations have a certain efficiency, but they use part of the energy produced by the plant. Furthermore, they require a considerable amount of maintenance.
In the case of chimneys for the discharge of gases into the atmosphere in a natural manner, that is without using evacuation machines such as a fan, static ventilators are used mounted on the outlet orifice of the chimney.
There already exist flue terminals consisting of a lower unit and of a superposed upper unit that are both hollow, circular, co-axial and rigidly fixed to each other some distance apart. The lower unit of the flue terminal comprises a lower base and a lower bonnet, shaped approximately like a truncated cone, linked rigidly to each other by their large common base, and through which passes a co-axial pipe rigidly fixed to them both and which opens onto the area lying between the upper and the lower units by means of an outlet through which the gases flow. The upper unit consists of an upper base and an upper bonnet both approximately conical in shape, rigidly fixed to each other by their large common base.
These flue terminals first purpose is to faciliate the removal of fluid gases from the outlet of the conduit extending from the chimney above which the device is fitted.
These flue terminals are so designed as to make use of the sucking action of a Venturi tube. The pipe through which the fluid gases are fed opens onto the space which lies between the lower and the upper units of the flue. The flow of wind in the space which lies between the lower and upper units is similar to that of a Venturi tube, and fluid gases are drawn from the point of outlet of these gases.
These flue terminals are generally speaking efficient when there is a wind blowing but their design does not take into account the free passage area which lies between the lower and upper units, namely the free flow section peripheral to the gases which are to be disposed of. However, this free passage area plays a very important part particularly when the flue terminal is not subjected to the action of the wind, in calm weather in fact. When this is the case, a very important pressure loss occurs which decreases the speed of the vertical ejection of the gases to be removed.
Existing flue terminals do indeed protect from rain the outlet of fluid gas and prevent rain from entering the flue. However they are not designed to protect the outlet from rain falling at certain angles to the vertical axis of the conduit extending from the chimney. Neither are they designed to operate when the wind in blowing at an ascending or descending angle from the horizontal axis.
In other respects these flue terminals are not designed to effect a fixed nominal capacity of fluid gases actually disposed of whatever the speed of the wind may be. However, it has been found that where the gas undergoes a forced flow for example owing to the presence of a powerful fan at the foot of the chimney, or when the gas is the exhaust gas of an engine, the suction effect of a static ventilator is no longer desired as it can no longer have a notable result in view of the fact that the pressure of the gas resulting from its forced flow is considerably greater than the pressure drop provided by the static ventilator.
Experiments carried out by the applicant have shown in a completely unexpected and surprising manner that a device which overall has a general shape similar to that of a static ventilator may, when fitted to the orifice for the outlet into the atmosphere of a forced flow of a gas, fulfil a new function, the effect of which is to promote the penetration of the gas into the ambient atmosphere.
The applicant has ascertained that a stream of gas under pressure and at high speed undergoes very powerful deceleration when it reaches the outlet orifice of a pipe in order to penetrate a medium such as the atmosphere. From the outlet orifice, the stream spreads out and the speed and pressure of the gas decrease as it moves away from the orifice until it ultimately attains the speed and pressue of the ambient atmosphere and mixes with the latter. A considerable pressure drop which is equivalent to a counter-pressure occurs at the outlet orifice. This pressure drop is due, on the one hand, to a transverse contraction of the stream and, on the other hand, to turbulence of the medium which this stream penetrates. The result of this is that the effective and useful speed and pressure are lower than those provided by an evacuation machine such as the fan, that is the effective performance of this machine is decreased.